1. Technical Field
The present invention relates to a technique of controlling a light emitting element, such as an organic light emitting diode.
2. Related Art
Light emitting devices using active elements, such as thin film transistors, for controlling a current (hereinafter, referred to as a driving current) supplied to a light emitting element have been proposed. FIG. 18 shows the arrangement of a driving transistor TDR and a light-emission control transistor TEL on a path through which a driving current IDR flows, the arrangement being disclosed in, for example, U.S. Pat. No. 6,229,506 and JP-A-2003-22049. The driving transistor TDR generates the driving current IDR according to the gate potential. The light-emission control transistor TEL, arranged between the driving transistor TDR and a light emitting element E, switches to the ON state for a predetermined period (hereinafter, referred to as a light emitting period), thus permitting supply of the driving current IDR into the light emitting element E.
Although the operating points of most of the driving transistors TDR are set so as to lie within a saturation region, the driving current IDR is changed in accordance with the drain-source voltage of the corresponding driving transistor TDR by the channel length modulation effect. On the other hand, the electrical characteristics of each light emitting element E include errors (e.g., an error from a design value and a variation between elements). For example, the relationship between the driving current IDR and the voltage across the light emitting element E may differ from element to element. The difference in voltage across the light emitting element E between the elements leads to a fluctuation in drain-source voltage between the driving transistors TDR. Unfortunately, even when the gate potentials of the respective driving transistors TDR are set to the same value, the driving current IDR supplied to each light emitting element E (therefore, the light intensity thereof) differs from element to element in accordance with its electrical characteristics.